1. Field of Invention
The present invention relates to an organic EL display device provided with organic EL (electroluminescence) elements that operate as display elements.
2. Description of Related Art
An organic EL element is a self-luminescent element having a structure in which at least one organic light emitting layer is placed between a cathode and an anode. The organic EL element can be driven with a direct current of about 3 V. It is possible to fabricate elements of a variety of light emitting colors. Because an organic EL element has many advantages as a display element, such as the fact that it has a faster response and a wider viewing angle than a liquid crystal display element, it can be used commercially for a variety of diverse applications, such as a pixel or the light source of a display device.
An organic EL panel provided with such organic EL elements, operating as display elements, is manufactured, for example, as follows.
First, on a transparent glass substrate, a transparent conductive thin film for an anode is formed. Next, by performing photolithography and etching the thin film, an anode of an organic EL element (formed with a pattern corresponding to multiple light emitting sections), an anode terminal, a cathode terminal, and wiring between the anode and the terminal are simultaneously patterned.
Next, the glass substrate surface of the parts other than the light emitting sections of the anode and the terminal section are covered with an insulation layer. Then, in the display area (area including all of the light emitting sections and excluding the terminal section) of the glass substrate surface, a hole injection layer and an organic light emitting layer are formed.
Subsequently, a cathode made of metallic thin film is formed on the entire surface of the display area of this glass substrate surface. The cathode is formed with its plane adjusted to the display area, and a pattern having a projection that protrudes from the plane to the outside of the display area, so that the projection is in contact with the cathode terminal.
Thus, in a conventional organic EL panel, only one cathode Terminal is formed on the substrate surface on the entire surface of the display area. Therefore, because an organic EL panel with a relatively large display area also has a large cathode area, a voltage difference is created between a position close to the terminal and another position far from the terminal inside the cathode surface. Namely, a voltage drop easily occurs inside the cathode.
As a result, the amount of electric current provided to the organic EL element inside the display area easily becomes uneven.
Therefore, the uniformity of luminosity within the display area of large, conventional, organic EL elements can possibly be enhanced.
The present invention addresses the above problems associated with the related art technology, and its object is to provide an organic EL element which exhibits excellent uniformity of luminosity, even if the display area is relatively large.
In order to solve the problem as described above, an organic EL display device in accordance with a first aspect of the invention is provided which includes a layered structure, having an organic light emitting layer between electrode layers formed on a substrate. A first electrode layer, which is one of the electrode layers, is formed in a pattern corresponding to a plurality of light emitting sections. A second electrode layer, which is another electrode layer, is placed on the entire display area. The first terminal connected to the first electrode layer and the second terminal connected to the second electrode layer are formed outside of the display area on the substrate. A plurality of second terminals are formed on the substrate. The second electrode layer is connected to multiple second terminals.
According to the first aspect of the organic EL display device of the present invention, because the second electrode layer is connected to multiple second terminals, compared to cases where it is connected to one second terminal, it is difficult for a voltage drop to occur inside the second electrode layer. Thus, the amount of current provided to the organic EL elements is easily made uniform inside the surface of the display area.
The present invention further provides an organic EL display device, in accordance with a second aspect, which includes a layered structure having an organic light emitting layer, between electrode layers, formed on a substrate. A first electrode layer, which is one of the electrode layers, is formed in a pattern corresponding to a plurality of light emitting sections, and has multiple first electrodes. A second electrode layer, which is another electrode layer, is placed so that it covers the entire portion of the display area where the first electrode is formed. A first terminal connected to the first electrode layer and a second terminal connected to the second electrode layer are formed outside the display area on the substrate. The second electrode layer includes a plurality of second electrodes. A plurality of second terminals are formed on the substrate. The plurality of second electrodes are connected respectively to different second terminals.
According to the second aspect of the organic EL display of the present invention, by dividing the second electrode layer into multiple second electrodes, it is difficult for a voltage drop to occur within the second electrode layer. Thus, the amount of current provided to the organic EL elements is easily made uniform within the surface of the display area.
Also, by connecting the plurality of second electrodes respectively to different second terminals, the amount of current provided to the second electrodes can be made to be different from one another.
The present invention also covers an embodiment of an organic EL display, where the substrate is transparent, the first electrode layer is a transparent anode layer formed on the substrate side, and the second electrode layer is a cathode layer.
The present invention also covers an embodiment of an active matrix type organic EL display, where the first electrode and an organic light emitting layer are formed as a matrix, and the second electrode layer is formed as the common electrode, and an organic EL display where the second electrode layer is transparent.